Context. The annihilation of positrons in the Galaxy's interstellar medium produces characteristic gamma-rays with a line at 511 keV. This gamma-ray emission has been observed with the spectrometer SPI on ESA's INTEGRAL observatory, confirming a puzzling morphology with bright emission from an extended bulge-like region, while emission from the disk is faint. Most known or plausible sources of positrons are, however, believed to be distributed throughout the disk of the Milky Way. Aims. We aim to constrain characteristic spectral shapes for different spatial components in the disk and bulge using data with an exposure that has doubled since earlier reports. Methods. We exploit high-resolution gamma-ray spectroscopy with SPI on INTEGRAL based on a new instrumental background method and detailed multi-component sky model fitting. Results. We confirm the detection of the main extended components of characteristic annihilation gamma-ray signatures, altogether at 58σ significance in the 511 keV line. The total Galactic 511 keV line intensity amounts to (2.74 ± 0.25) × 10 −3 ph cm −2 s −1 for our assumed model of the spatial distribution. We derive spectra for the bulge and disk, and a central source modelled as pointlike and at the position of Sgr A*, and discuss spectral differences. The bulge (56σ) shows a 511 keV line intensity of (0.96 ± 0.07) × 10 −3 ph cm −2 s −1 together with ortho-positronium continuum equivalent to a positronium fraction of (1.080 ± 0.029). The twodimensional Gaussian that represents the disk emission (12σ) has an extent of 60 +10 −5 degrees in longitude and a rather large latitudinal extent of 10.5 +2.5 −1.5 degrees; the line intensity is (1.66 ± 0.35)×10 −3 ph cm −2 s −1 with a marginal detection of the annihilation continuum and an overall diffuse Galactic continuum of (5.85 ± 1.05) × 10 −5 ph cm −2 s −1 keV −1 at 511 keV. The disk shows no flux asymmetry between positive and negative longitudes, although spectral details differ. The flux ratio between bulge and disk is (0.58 ± 0.13). The central source (5σ) has an intensity of (0.80 ± 0.19) × 10 −4 ph cm −2 s −1 .

The Guide Star Catalog II (GSC-II) is an all-sky database of objects derived from the uncompressed Digitized Sky Surveys that the Space Telescope Science Institute has created from the Palomar and UK Schmidt survey plates and made available to the community. Like its predecessor (GSC-I), the GSC-II was primarily created to provide guide star information and observation planning support for Hubble Space Telescope. This version, however, is already employed at some of the ground-based new-technology telescopes such as GEMINI, VLT, and TNG, and will also be used to provide support for the James Webb Space Telescope (JWST) and GAIA space missions as well as the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, one of the major ongoing scientific projects in China. Two catalogs have already been extracted from the GSC-II database and released to the astronomical community. A magnitude-limited (R F = 18.0) version, GSC2.2, was distributed soon after its production in 2001, while the GSC2.3 release has been available for general access since 2007. The GSC2.3 catalog described in this paper contains astrometry, photometry, and classification for 945,592,683 objects down to the magnitude limit of the plates. Positions are tied to the International Celestial Reference System; for stellar sources, the all-sky average absolute error per coordinate ranges from 0. 2 to 0. 28 depending on magnitude. When dealing with extended objects, astrometric errors are 20% worse in the case of galaxies and approximately a factor of 2 worse for blended images. Stellar photometry is determined to 0.13-0.22 mag as a function of magnitude and photographic passbands (R F , B J , I N ). Outside of the galactic plane, stellar classification is reliable to at least 90% confidence for magnitudes brighter than R F = 19.5, and the catalog is complete to R F = 20.

Only a few of the dozen or so stellar-mass black holes have been observed away from the plane of the Galaxy 1 . Those few could have been ejected from the plane as a result of a "kick" received during a supernova explosion, or they could be remnants of the population of massive stars formed in the early stages of evolution of the Galaxy. Determining their orbital motion should help to distinguish between these options. Here we report the transverse motion (in the plane of the sky) for the black hole Xray nova XTE J1118+480 (refs 2-5), from which we derive a large space velocity. This X-ray binary has an eccentric orbit around the Galactic Centre, like most objects in the halo of the Galaxy, such as ancient stars and globular clusters. The properties of the system suggest that its age is comparable to or greater than the age of the Galactic disk. Only an extraordinary "kick" from a supernova could have launched the black hole into an orbit like this from a birth place in the disk of the Galaxy.The high galactic latitude (l = 157.7 • , b = +62.3 • ) X-ray nova XTE J1118+480 was discovered 2 with the RXTE All-Sky Monitor on 2000 March 29. It exhibited slow outbursts that lasted ∼7 months with a peak X-ray luminosity of 4 x 10 35 (D/kpc) 2 erg s −1 and energy spectra typical of black hole binaries in low/hard state 6 . From observations of the ∼19 mag optical counterpart 3 in quiescence a mass function for the compact object f(M) ∼ 6.0±0.4 M ⊙ and an average distance of ∼ 1.85±0.36 kpc were determined 4,5 . For ∼100 days the source exhibited a steady and slowly variable unresolved radio counterpart 7,8 with persistent inverted radio spectrum, which is interpreted as optically thick emission from a compact, powerful synchrotron jet 8,9 , that could have a size ≤0.03 AU 9 . 1To measure the transverse motion on the plane of the sky of XTE J1118+480 we carried out observations of the radio counterpart with the Very Long Baseline Array (VLBA) at 15.4 GHz (λ2 cm) and 8.4 GHz (λ3.6 cm) on 2000 May 4 and July 24; afterwards it faded below detection. In both epochs the source was unresolved by the synthesized beams of 1×0.6 milli arc sec (mas) and 2×1 mas respectively, which correspond to physical dimensions smaller than ∼0.7 D/kpc AU, and a brightness temperature ≥10 9 K. Because of the high galactic latitude and low column of interstellar gas along the line of sight (N H ∼ 10 20 cm −2 ) 10 , the VLBA images are relatively unaffected by Galactic electron scattering, allowing us to determine in each epoch the position of the compact, unresolved radio source with relative errors ≤0.35 mas.The observations were done in cycles that included the target, the strong calibrator 3C273, a primary calibrator (Cal. 1) used as phase-reference source, and a second extragalactic calibrator (Cal.2). Their high elevation and good weather ensured that the phase connection was successful. The epoch, source, frequency, bandwidth, position, and flux for the VLBA observations of XTE J1118+480 and the two extragalactic sources used as references ...

Abstract. We have used the Hubble Space Telescope to measure the motion in the sky and compute the galactocentric orbit of the black hole X-ray binary GRO J1655-40. The system moves with a runaway space velocity of 112 ± 18 km s −1 in a highly eccentric (e = 0.34 ± 0.05) orbit. The black hole was formed in the disk at a distance greater than 3 kpc from the Galactic centre and must have been shot to such an eccentric orbit by the explosion of the progenitor star. The runaway linear momentum and kinetic energy of this black hole binary are comparable to those of solitary neutron stars and millisecond pulsars. GRO J1655-40 is the first black hole for which there is evidence for a runaway motion imparted by a natal kick in a supernova explosion.